WO2009072955A1

WO2009072955A1 - New chemical compound suitable for use as a plasticiser in explosive and propellant compositions

Info

Publication number: WO2009072955A1
Application number: PCT/SE2008/000686
Authority: WO
Inventors: Stefan Ek; Patrick Goede; Nikolaj Latypov; Lee Yiew Wang; Yang Gou-Ying
Original assignee: TotalFoersvarets Forskningsinstitut FOI; Defence Science and Technology Agency
Current assignee: TotalFoersvarets Forskningsinstitut FOI; Defence Science and Technology Agency
Priority date: 2007-12-06
Filing date: 2008-12-05
Publication date: 2009-06-11
Anticipated expiration: 2010-06-06
Also published as: SE531839C2; SE0702711L

Abstract

The compound 4, 4-dinitro-l, 7-diazidoheptane. Use of the compound as a plasticiser in a binder system for a propellant or an explosive composition, e.g. a binder system based on GAP, BAMO or BAMO/GAP, and a plasticiser comprising the compound.

Description

New chemical compound suitable for use as a plasticiser in explosive and propellant compositions

The invention relates to a new chemical compound, more specifically a new diazido-compound, a plasticiser comprising the compound and the use of the compound as a plasticiser in a polymer binder system for a propellant or explosive composition.

One of the key steps in the improvement of explosive charges and propellants is the development of new energetic ingredients. The aim of such additives is to enhance the performance as well as the mechanical properties of propellants and plastic bonded explosives (PBX) , in comparison with the current binders and/or plasticisers . The reason for our interest in energetic plasticisers is the dissatisfactory mechanical properties of commercially available, energetic binders. The polar groups in the molecular structure of these compounds render them increasingly viscous and elevate their glass transition temperatures. The rise in glass transition temperature downgrades the low temperature properties, which are especially important for missile propellants. The higher viscosity can result in processibility problems .

The inert binders currently in use have excellent mechanical properties. However, they contain little energy and require high solids loading to have a sufficient performance. The disadvantages of available energetic polymers are mentioned above. Hitherto, the known energetic plasticisers have inconveniences such as low thermal stability, low energy content, high migratory ability and sometimes, they dissolve the filler. The low thermal stability can be remedied with stabilisers, but finding a molecule that is stable as such is a very interesting area of research.

Recently, attention has been directed towards gem- dinitro-based plasticisers . Great effort has been put into industrial-scale production of BDNPF/A and to develop similar mixtures containing formals of other gem- dinitro alcohols. The research of the last decade has been focused mostly on azido-plasticisers . These considerations focused our efforts on structures with energetically derivatised gem-dinitro compounds. One advantage of the azido group is its high energy content.

According to the invention a new diazido-compound has been synthesized, viz

4, 4-dinitro-l, 7-diazidoheptane (DNHDA) having the formula

DNHDA has a density of 1.51 g/cm³, an oxygen balance of - 90.7% and a calculated heat of formation of -123.38 kJ/mol . The glass transition temperature of the compound is -89.7° C. The performance of DNHDA in combination with good plasticising ability, low sensitivity and high chemical compatibility render the compound interesting as an ingredient in propellants as well as explosives. The compound has, in contrast to several other plasticisers, very good thermal stability. Another difference from many other commercially available energetic plasticisers is the low glass transition temperature. DNHDA can be used as a plasticiser alone or in combination with other plasticisers and form a part of the polymer binder system of propellant and explosive compositions, e.g. plastic bonded explosives (PBX), composite gun propellants and composite rocket propellants .

PBX contains a high explosive like RDX, HMX, CL-20 and a polymer binder system. Non-energetic binders like HTPB have been used for a long time. Energetic binders, such as polyglycidyl azide (GAP) , have been used in experimental pressed and cast-cured PBXs for underwater purposes, but they have most likely not reached military use yet. Energetic plasticisers are more commonly used in PBXs. Examples of such plasticisers are BDNPA/F [bis (2,2- dinitropropyl) acetal and bis (2, 2-dinitropropyl) formal] , BTTN [1,2, 4-butanetriol trinitrate], TMETN [trimethylolethane trinitrate] , TEGDN [triethyleneglycol dinitrate] , FEFO [bis (2-fluoro-2, 2-dinitroethyl) formal] and KlO [dinitroethylbenzene/2, 4, 6-trinitroethylbenzene (65/35)], also called Rowanite 8001.

Composite gun propellants contain an oxidiser and a binder system. In modern Low Vulnerability Ammunition

(LOVA) gun propellants high energetic compounds like RDX and HMX are frequently used as oxidisers. A number of polymer binder systems including plasticisers have been used. New combinations of energetic binders and plasticisers are constantly tested in order to increase the performance without jeopardizing the LOVA properties. Composite rocket propellants also contain an oxidiser and a binder system. Oxidisers commonly used include non- metal, alkali metal, and alkaline earth metal nitrates, nitrites, dinitramides, perchlorates, chlorates, and chlorites . More specific examples of oxidisers for rocket propellants are ammonium nitrate, potassium nitrate, ammonium perchlorate, potassium perchlorate, ammonium dinitramide and potassium dinitramide. The binder can be an inert or an energetic polymer or any other in the art well known binder system.

By thermochemical calculations {Cheetah 2.0, Fried, L. E.; Howard, W. M.; Souers, P. C; Lawrence Livermore National Laboratory, 1998.) estimations of the energetic properties of DNHDA have been made. Explosive performances are computed for the pure molecule in term of relative work compared to HMX (V/V₀=2.2) . Propellant performance is calculated as specific impulse of the pure compound and comparison is made with a conventional rocket propellant consisting of ammonium perchlorate in a binder of hydroxyl-terminated polybutadiene, AP/HTPB (85/15 weight %) .

Table 1. Calculated performance of pure DNHDA in comparison with HMX

The following performance has been calculated for different propellant formulations based on 70 vol% ammonium dinitramide (ADN) and 30 vol% binder. The binders are hydroxyl-terminated polybutadiene (HTPB) , poly-3, 3-bis (azidomethyl) oxetane/glycidyl azide polymer (BAMO/GAP) , BAMO/GAP containing the known plasticiser dinitroethylbenzene (DNEB) and BAMO/GAP containing the inventive plasticiser 4, 4-dintro-l, 7-diazidoheptane (DNHDA) . 10 vol% of the binder is the plasticiser. The BAMO/GAP-binders are crosslinked with toluendiisocyanate (TDI) and the binder without plasticiser consists of (BAMO/GAP/TDI) 64.8/24.0/11.2 weight%. P_c = 68 atm, P_e= 1 atm, Loading density 0.2 g/cm³. Code: Cheetah 2.0

Table 2. Comparison of calculated properties of different formulations

It can be seen in Table 1 that DNHDA is no powerful explosive. However, the calculations show that a formulation with the inventive plasticiser has an impulse and force better than current NC-based propellants, which normally are in the ranges 200-230 s and 1100-1200 J/g, respectively. The calculations do also show that DNHDA, in contrast to dinitroethylbenzene (DNEB) , raises the performance of a BAMO/GAP formulation.

The new compound can be prepared by a Michael reaction between a metal salt of dinitromethane and a suitable Michael acceptor, such as acrylic acid or methyl acrylate. In the latter case, the formed ester is subjected to hydrolysis under acidic conditions. Reduction of the acid yields the corresponding diol, whose hydroxyl groups are converted into suitable leaving groups. Substitution with a metal azide produces the final product .

The preparation of the compound is illustrated by the following examples.

NMR spectra were recorded on a Bruker 400 MHz spectrometer. Melting points and decomposition points were determined on a Mettler DSC 30. Elemental Analyses were carried out by H. Kolbe Mikro Analytisches Laboratorium, Mϋhlheim an der Ruhr, Germany. The densities were measured with a pycnometer.

Example 1 Preparation of 4 , 4-Dinitro-l, 7-heptanedioic acid dimethyl ester .

Moist potassium dinitromethane, corresponding to 43.2 g (0.30 mol, 1 eq) , was mixed with 350 mL deionised water. The mixture was heated to 40 °C. Methyl acrylate (139.2 g, 1.62 mol, 5.4 eq) was added over an hour. The reaction was left under stirring at 40 ⁰C overnight. The aqueous solution was extracted with ethyl ether (3 x 100 mL) . The combined organic phases were dried with Na2SO₄ and concentrated in vacuo, which resulted in a viscous oil. Upon addition of methanol, the oil crystallised. The crude product was recrystallised from ethanol . This yielded 51.2 g white, needle-shaped crystals of high purity. ¹H NMR CDMSO-Ci₆; 5=3.613 (6H, s) , 2.85 (4H, t, J=8) , 2.49 (4H, t, J=I.2); ¹³C NMR (DMS0-d₆) 5=171.8, 125.0, 52.7, 29.5, 28.4.

Example 2 Preparation of 4 , 4-Dinitro-l, 7-heptanedioic acid.

Dimethyl-4 , 4-Dinitroheptanedioate (51.2 g, 0.18 mol) was suspended in 400 mL 18 % hydrochloric acid. The mixture was refluxed overnight. Upon cooling of the solution, the product crystallised to yield white crystals. The precipitate was filtered off and washed with water. This yielded 34.5 g white crystals. The mother liquor was concentrated and left in the fridge overnight. A second crop of crystal was filtered off. The total yield was 43.7 g (95 %) . ¹H NMR (DMSO-d₆) 5=11.97 (2H, bs) , 2.79 (4H, t, J=I.5) _r 2.37 (4H, t, J=I.5); ¹³C NMR (DMSO-d₆) 5=171.90 (s), 122.22 (s) , 28.92 (t), 27.80 (t) .

Example 3

Preparation of 4, 4-Dinitro-l, 7-heptanediol (DNHDO) . (Caution: A large flask is recommended as the reaction could be initiated suddenly with vigorous release of hydrogen gas after the addition of TFA into the reaction mixture.) Trifluoroacetic acid (2.28 g, 20 mmol) was added dropwise into a solution of 4, 4-dinitroheptanedioic acid (2.0 g, 8 mmol) and NaBH₄ (0.756 g, 20 mmol) in dried THF (40 mL) at 0-5 °C in 15 min. To prevent a vigorous reaction, a small mount of trifluoroacetic acid could be added into the mixture for initiation purpose. Once the reaction was initiated and generation of hydrogen gas was observed, the remaining trifluoroacetic acid was then added dropwise. After the completion of the addition, the reaction mixture was slowly warmed up to room temperature and stirred at this temperature for 24 h. Dilute aqueous HCl (20 mL, 1 M) was added to quench the reaction. The reaction solution was then extracted with ethyl acetate (3 x 20 mL) . The organic phases were combined, washed with water (3 x 10 mL) , dried over Na₂SO₄ and evaporated into a white solid. Pure product can be obtained by recrystallization from methylene chloride. (1.32 g, 74.3 %) , m.p. 71.5 -72 °C (lit: 74.5-75 ⁰C), ¹H NMR (δ, ppm, CD₃CN) : 1.44 (m, 4 H), 2.58 (m, 4 H), 2.78 (t, 2 H, J_HH = 5.2 Hz), 3.53 (q, 4H, J_HH = 5.6 Hz) .

Example 4

Preparation of 4 , 4-dinitro-l, 7-dichloroheptane (DNHDC) . SOCl₂ (2.38 g, 20 mmol) was added dropwise into the mixture of 4 , 4-dinitro-l, 7-heptanediol (1.11 g, 5 mmol) and pyridine (0.79 g, 10 mmol) at 0- 5 ⁰C. After the completion of the addition, the reaction mixture was slowly warmed up to room temperature and then heated and refluxed for 4 h under nitrogen atmosphere. The light brown reaction mixture was cooled down to room temperature and excess SOCl₂ was removed under reduced pressure. The residue obtained was then subjected to flash chromatography on silica gel using CHCI₃ as eluent to give light yellow oil. (1.10 g, 85.0 %), ¹H NMR(δ, ppm, CD₃CN) : 1.77 (m, 4 H), 2.66 (m, 4 H), 3.65 (t, 4H, J_HH = 6.0 Hz) .

Example 5

Synthesis of 4 , 4-dinitro-l, 7-diazidoheptane (DNHDA) : The mixture of 4, 4-dinitro-l, 7-dichloroheptane (1.04 g, 4 mmol) , sodium azide (1.04g, 16 mmol) and NaI (0.15 g, 1.0 mmol) in DMSO (20 mL) was heated at 50 °C for 16 h. The reaction mixture was cooled down to room temperature and diethyl ether (60 mL) was added. The organic phase was washed with water (20 mL x 4 ) to remove DMSO, dried over Na₂SO₄, passed through a short silica gel column and evaporated to give a light yellow oil. (0.82 g, 75.4 %) , Tg: - 89.7 ⁰C, ¹H NMR (δ, ppm, CD₃CN) : 1.58 (m, 4 H), 2.61 (m, 4 H), 3.43 (t, 4H, J_HH = 6.6 Hz); elemental analysis: calculated for C₇H₁₂N₈O₄: C, 30.88; H, 4.44; N: 41.16; found: C, 30.81; H, 4.40; N, 41.06.

Claims

1. The compound 4, 4-dinitro-l, 7-diazidoheptane.

2. A plasticiser for use in a polymer binder system for an explosive or propellant composition, characterised in that it comprises 4, 4, -dinitro-1, 7-diazidoheptane.

3. Use of 4 , 4, -dinitro-1, 7-diazidoheptane as a plasticiser in a polymer binder system for an explosive or propellant composition.

4. Use according to claim 3, characterised in that the binder system is based on a glycidyl azido polymer (GAP) .

5. Use according to claim 3, characterised in that the binder system is based on a poly-3,3- bis (azidomethyl) oxetane (BAMO) .

6. Use according to claim 3, characterised in that the binder system is based on a poly-3,3- bis (azidomethyl) oxetane/glycidyl azido polymer (BAMO/GAP) .